In a parallel configuration of Uninterrupted Power Supply (UPS) system, each UPS unit of the UPS system is connected to a load in parallel. A primary aim of the parallel configuration of UPS system is to share load current equally between each UPS unit. Thus, when any of the UPS unit is faulty, remaining UPS units share amount of current generated by the faulty UPS unit equally for supplying to the load. Conventional UPS systems has a common load bus and a communication line connected between each of the UPS units.
The communication line carries data which is required for equal power sharing among parallelly connected units. Typically, a UPS system comprises a master UPS unit and plurality of slave UPS units. The master UPS unit controls voltage level of common load bus. The slave units operate in current control mode to share the power based on the given reference value. Further, all UPS units are connected at common load bus.
When a slave UPS unit is faulty, the master UPS unit momentarily bears current generated by the faulty slave UPS unit. Further, the master UPS unit communicates to other slave UPS unit about number of the slave UPS down. In addition, the master UPS units communicates the amount of current to be generated by each of the remaining slave UPS units using the communication line, thereby sharing the load current equally. However, when the communication line is faulty, the conventional system does not provide a solution for sharing the load current. Hence the communication line failure affects the reliability of the system.
FIG. 1 shows a conventional parallel UPS system 100 for distributing load current. Here, a communication line 106 is provided to connect all the UPS units. When a slave UPS unit 1023 is faulty, a master UPS unit 101 bears current supplied by the faulty slave UPS unit 1023. Now, if the communication line 106 is faulty, the UPS system 100 does not provide alternate means to communicate about faulty slave UPS units to other units in the UPS system 100. Thus, the master UPS unit 101 continues to supply additional current to a load 104. When multiple slave UPS units become faulty, and the communication line 106 is also faulty, then, the master UPS unit 101 may be overloaded by supplying current to compensate for the faulty slave UPS units 102. As a result, efficient sharing of load current does not take place in conventional UPS system 100.
The information disclosed in this background of the disclosure section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.